In fossil-fuel burning power plants and similar boilers, soot deposits collect on the heat transfer pipes, and buildup of such deposits can seriously interfere with proper heat transfer efficiency. Such power plants and boilers are provided with soot blower assemblies for permitting cleaning of soot from the exterior of the heat transfer pipes. Such assemblies typically include an elongate hollow tubular lance which has steam discharge nozzles adjacent the leading end thereof, which lance is moved inwardly into the heat transfer chamber in generally parallel relationship to one or more adjacent heat transfer pipes so as to eject steam against these pipes to dislodge the soot therefrom. The lance in turn is rotatably and axially slidably supported on an elongated and cantilevered stationary steam supply pipe which projects coaxially into the lance, and a packing assembly cooperates between the lance and steam supply pipe to create a sealed relationship therebetween, while at the same time permitting the lance to be axially and rotatably advanced into the heat exchange chamber when removal of soot is desired. Each power plant or boiler typically has a large number of such soot removal devices associated therewith, and the lance of each device must be cantilevered inwardly and moved through a significant extent which may be as much as 40 feet.
At present, conventional soot blowers employs a plurality of packings disposed axially adjacent one another for cooperation between the lance and steam supply pipe. These packings are able to withstand the high temperature of the steam, which is typically supplied at a temperature of about 600.degree. F. However, inasmuch as the soot blowers are activated only periodically, such as once over a several hour interval, the overall soot blower experiences severe differential thermal expansion characteristics when activated due to significant temperature changes when the superheated steam is supplied thereto. This thus makes sealing of the lance to the steam supply tube, while still permitting relative axial and rotary movement therebetween, difficult. While packings have been used with at least limited success, nevertheless packings do possess disadvantages. It has been observed that use of packings in this environment requires constant adjustment in the packing compression in order to achieve a proper seal while still permitting relative movement between the lance and steam supply pipe. If the packing compression is too little, then leakage occurs, and conversely if the compression is too high, then proper movement of the lance is difficult to achieve. The packings have also been observed to cause undesirable wear on the steam supply tube in view of the significant compression required of the packing in order to achieve a desired seal. Even though the use of packings in this environment has possessed recognized disadvantages, nevertheless such packings have been used for many years and continue to be used in this environment in view of the lack of other satisfactory solutions.
Accordingly, it is an object of this invention to provide an improved seal-bearing structure for cooperation in a soot blower assembly, which seal-bearing structure permits elimination of the conventional packings and hence overcomes the disadvantages associated with the prior art structures.
In the present invention, there is provided an improved soot blower assembly wherein an elongated steam discharge lance exteriorly surrounds and is both axially and rotatably movable relative to an elongate cantilevered steam supply tube. The rearward end of the lance includes a tubular housing which supports the lance for axial displacement along a frame, and the rear of the lance is also provided with a seal-bearing arrangement which externally surrounds and cooperates with the cantilevered steam supply tube to concentrically support the steam supply tube within the lance as the latter is displace axially therealong, while at the same time providing a steam-retaining seal therebetween. This seal-bearing arrangement includes a generally elongate bearing sleeve which is disposed annularly between the lance and supply tube. This elongate bearing sleeve, when the soot blower is deactivated so as to be at normal temperature, has an inner annular clearance where it surrounds the supply tube. The elongate sleeve bearing is also provided with a split extending axially and radially therethrough. The sleeve bearing is preferably of bronze or similar bearing material so as to not require lubrication. This bearing sleeve, due to the different thermal expansions and the rapid heat up of the supply tube when steam is supplied thereto, enables the supply tube to expand into engagement with the sleeve bearing, and expansion of the latter is compensated for by the axial slit, whereby the sleeve bearing maintains a rotatable running clearance with the steam supply tube due to permissible circumferential expansion of the split bearing relative to the surrounding lance. The split bearing is disposed on the upstream pressurized steam side of a seal which includes at least one, and preferably two, serially disposed rod-type wiper seals disposed in sealing engagement with the steam supply tube and with a surrounding insert member which is fixed within the lance.
With the improved soot blower assembly of this invention, as briefly described above, the lance can be axially extended and simultaneously slowly rotated about the cantilevered steam supply tube over long axial distances, and as the lance is extended forwardly during the soot blowing operation, the seal-bearing arrangement rotatably and axially bearingly supports and sealingly engages the cantilevered steam supply tube so as to effectively maintain the latter concentric within the lance, particularly when approaching the cantilevered free end of the steam supply tube, so as to overcome tube droop and hence permit successful performance of the soot blowing operation.
Other objects and purposes of the invention will be apparent to persons familiar with structures of this general type upon reading the following specification and inspecting the accompanying drawings.